The twofold purpose of this research is to study the psychobiologic mechanisms by which physical restraint produces gastric erosions in the rat, and the mechanisms by which early loss of the mother modifies the animals' predisposition to develop these stress-induced gastric lesions later in life. Our previous work has shown that if rat pups are separated from the mother at day 21 (the customary age) and then restrained at day 30, the incidence of erosion formation is near zero. But if the animals are separated from the mother at day 15 and then restrained at day 30, the incidence of erosion formation is near 100%. This model system will anable us to study two specific problems in detail. First, by using day 15 and day 21 as separation ages and day 30 as the test age we can generate high risk and low risk groups which can be compared under similar test conditions. These comparisions of the animals' response to restraint will include selected parameters of behavior, gastric physiology, and the central and peripheral regulatory processes relating them. This two-group strategy represents a departure from much prior work on animal models of gastric erosions in which the "comparison" group received no stress or a different stress from the "experimental" group. Second, a series of analytic experiments will be proposed to elucidate specific factors in the early separation that increase subsequent lesion vulnerability at day 30. Behavioral factors in the mother-pup diad, nutritional factors, and the possibility of behavioral nutritional interaction will be investigated. Through such experiments we hope to be able to begin to integrate behavioral and physiological factors related to lesion formation during restraint, and to integrate longitudinally the mechanisms through which early separation modifies later lesion vulnerability.